1. Field of the Invention
The present invention relates to a recording ink composition, and more particularly to an aqueous recording color ink composition capable of producing color images on a sheet of plain paper by an ink-jet printing method, and suitable for an ink-jet printer, aqueous writing utensils, various kinds of recorders, and pen plotters. Also, the present invention relates to an ink-jet printing method using the above-mentioned recording ink composition.
2. Discussion of Background
Ink-jet printers have been widely utilized in recent years because of the advantages of low noise and low running cost, and color ink-jet printers capable of producing color images on a sheet of plain paper have also been on the market.
However, it is extremely difficult to obtain a color ink composition capable of meeting with the requirements for the produced image, for example, color reproduction, water resistance, light resistance, drying characteristics, prevention of blurring, and the reliability of ink-ejection. In particular, when the color images are produced using the ink-jet color printer, image blurring easily takes place in two-color-superimposed portions such as red, green, and blue color image portions, even though image clearness is sufficient in single color image portions formed by use of a yellow, magenta, or cyan color ink composition.
When the ink images deposited on a sheet of paper are dried without using any specific image fixing unit, the drying characteristics of the ink image are improved by increasing the penetrating properties of the ink through paper as described in Japanese Laid-Open Patent Application No. 55-29546. In this case, however, the improved penetrating properties of the ink through paper generate the problem of image blurring.
Japanese Patent Publication No. 60-23793 describes that a dialkylsulfosuccinic acid is contained in the ink composition as a surfactant, whereby the drying characteristics of the ink images can be improved and deterioration of image quality can be minimized. However, when such an ink composition is used for ink-jet printing, the diameters of picture elements of the obtained image considerably vary depending on the kind of image receiving sheet to be employed. The image density of the printed images is also considerably decreased. Further, if the ink composition is alkaline, this kind of surfactant is easily decomposed and the effect of the surfactant is diminishing during the storage of the ink composition.
Japanese Patent Publication No. 58-6752 discloses a quick-drying ink composition. By employing an ethylene oxide adduct having an acetylene bond as a surfactant in the ink composition, penetration of the ink is promoted to obtain quick-drying ink images with no image blur. However, the drying speed cannot be improved depending on the kind of dye used in the ink composition. For example, hydrophobic interaction between the surfactant and a direct dye such as xe2x80x9cDBK168xe2x80x9d (Trademark) inhibits the increase of drying speed.
Japanese Laid-Open Patent Application Ser. No. 56-57862 discloses an ink composition containing a strongly basic material. In the case where ink images are formed using this ink composition on an acidic paper which has been prepared using rosin as a sizing agent, the drying characteristics of the images can be improved. However, no improvement is observed in the drying characteristics of ink images when the ink images are formed on a paper manufactured using an alkyl ketene dimer or an alkenyl sulfosuccinic acid as the sizing agent. Even when acidic paper is employed, the drying characteristics of the two-color-superimposed image portion are not improved.
Japanese Laid-Open Patent Application No. 1-203483 discloses a recording ink composition comprising a polyhydric alcohol derivative and pectin. The pectin serves as a thickening agent for preventing the image blurring. However, the pectin is a nonionic material having hydroxyl group as a hydrophilic group, so that there is the shortcoming that ink ejection reliability is low when the printing operation is resumed after intermission.
Japanese Laid-Open Patent Application No.2-36276 discloses an ink composition comprising 2-propanol for improving the frequency response properties and the image fixing properties. However, this ink composition causes the problem of safety in terms of toxicity and flammability.
No pigment-containing ink composition of a penetrating type has been on the market. It has been considered that such a pigment-containing ink composition can be achieved only by using the commercially available surfactant xe2x80x9cSurfy-nolxe2x80x9d (Trademark), made by Air Products and Chemicals, containing a polysilanol group, and using butyl ether as a penetrating agent. However, butyl ether reacts with a pigment dispersant to form an agglomerate of pigment, and the above-mentioned surfactant xe2x80x9cSurfy-nolxe2x80x9d also tends to form an agglomerate of a pigment such as a functional-group-addition type carbon black.
A first object of the present invention is to provide a recording ink composition, in particular, an aqueous ink composition suitable for an ink-jet printing, with excellent penetrating properties, capable of producing ink images with excellent drying characteristics and minimum deterioration. Specifically, the first object is to provide a pigment-containing ink composition not by using xe2x80x9cSurfy-nolxe2x80x9d as a surfactant and butyl ether as a penetrating agent.
A second object of the present invention is to provide a method of recording images on an image-receiving medium. More specifically, the second object is to provide an ink-jet recording method with ink-ejecting reliability using a recording ink composition which is excellent from the view point of safety.
The first object can be achieved by a recording ink composition comprising a colorant insoluble and dispersible in water, water, a water soluble organic solvent, a wetting agent, 2-ethyl-1,3-hexanediol, and a surfactant selected from the group consisting of surfactants of formulas (I) to (V):
R1xe2x80x94Oxe2x80x94(CH2CH2O)mCH2COOxe2x88x92M+xe2x80x83xe2x80x83(I) 
wherein R1 is a straight-chain or branched alkyl group having 6 to 14 carbon atoms, M+ is a cation selected from the group consisting of alkali metal cation, quaternary ammonium cation, quaternary phosphonium cation, and alkanol amine cation, and m is an integer of 3 to 12, 
wherein R2 is a branched alkyl group having 5 to 16 carbon atoms, and M+ is a cation selected from the group consisting of alkali metal cation, quaternary ammonium cation, quaternary phosphonium cation, and alkanol amine cation, 
wherein R is a straight or branched carbon chain having 6 to 14 carbon atoms, and k is an integer of 5 to 20
Rxe2x80x94(OCH2CH2)nOH xe2x80x83xe2x80x83(IV) 
wherein R is a straight or branched carbon chain having 6 to 14 carbon atoms; and k is an integer of 5 to 20, and 
wherein Rxe2x80x2 is a carbon chain having 6 to 14 carbon atoms, and p and q are each an integer of 20 or less.
The second object can be achieved by a method of recording images on an image receiving medium, comprising the step of ejecting the above-described recording ink composition in the form of droplets from a recording head onto the image receiving medium, thereby forming images thereon.
The recording ink composition of the present invention comprises 2-ethyl-1,3-hexanediol, preferably in an amount of 0.1 to 7.0 wt. %, and at least one surfactant selected from the aforementioned surfactants of formulas (I) to (V), preferably in an amount of 0.1 to 5.0 wt. % of the total weight of the recording ink composition. As a result, the wettability of heating elements by the ink is improved, so that the ink ejection performance and the frequency response performance are stabilized. Furthermore, the problem of safety caused by the addition of 2-propanol, which would be used to achieve the ink ejection stability, can be solved by the present invention.
The surfactants (I) to (V) are as follows:
R1xe2x80x94Oxe2x80x94(CH2CH2O)mCH2COOxe2x88x92M+xe2x80x83xe2x80x83(I) 
wherein R1 is a straight-chain or branched alkyl group having 6 to 14 carbon atoms, M+ is a cation selected from the group consisting of alkali metal cation, quaternary ammonium cation, quaternary phosphonium cation, and alkanol amine cation, and m is an integer of 3 to 12, 
wherein R2 is a branched alkyl group having 5 to 16 carbon atoms, and M+ is a cation selected from the group consisting of alkali metal cation, quaternary ammonium cation, quaternary phosphonium cation, and alkanol amine cation, 
wherein R is a straight or branched carbon chain having 6 to 14 carbon atoms, and k is an integer of 5 to 20,
Rxe2x80x94(OCH2CH2)nOH xe2x80x83xe2x80x83(IV) 
wherein R is a straight or branched carbon chain having 6 to 14 carbon atoms, and k is an integer of 5 to 20, and 
wherein Rxe2x80x2 is a carbon chain having 6 to 14 carbon atoms, and p and q are each an integer of 20 or less.
In the formulas (I) and (II), the alkali metal cation represented by M+ is selected from the group consisting of Na+ and Li+; the quaternary ammonium cation represented by M+ is a cation represented by formula (VI), 
wherein R3 to R6 are each selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 4carbon atoms, and a halogenated alkyl group having 1 to 4 carbon atoms; the quaternary phosphonium cation represented by M+ is a cation represented by formula (VII), 
wherein R13 to R16 are each selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a hydroxyalkyl group having 1 to 4 carbon atoms, and a halogenated alkyl group having 1 to 4 carbon atoms; and the alkanolamin cation represented by M+ is a cation represented by formula (VIII), 
wherein at least one of R23 to R26 is a hydroxyalkyl group having 1 to 4 carbon atoms, and the other is selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, and a halogenated alkyl group having 1 to 4 carbon atoms.
As the colorant for use in the present invention, any inorganic and organic pigments can be used. The inorganic pigments are not particularly limited. For example, not only titanium oxide and iron oxide, but also carbon black manufactured by any conventional methods such as a contact method, a furnace method, and a thermal method can be employed.
Examples of the organic pigments are azo pigments including azo lake, insoluble azo pigment, condensation azo pigment, and chelate azo pigement; polycyclic pigments such as phthalocyanine pigment, perylene pigment, perinone pigment, anthraquinone pigment, quinacridone pigment, dioxazine pigment, thioindigo pigment, isoindolinone pigment, and quinophthalone pigment; dye chelate compounds such as basic dye chelate and acid dye chelate; nitro pigments; nitroso pigments; and aniline black.
Of the above-mentioned pigments, pigments having good affinity for water are preferably used in the present invention. It is preferable that the pigment have a particle size of 1 xcexcm or less, and more preferably 0.16 xcexcm or less. The pigment is preferably contained in the ink composition in an amount of 0.5 to 25 wt. %, more preferably 1 to 15 wt. %, and further preferably 1 to 10 wt. %.
Specific examples of the black pigments preferably used in the present invention include organic pigments such as carbon black (C.I. Pigment Black 7), i.e., furance black, lamp black, acetylene black, and channel black; copper oxide; iron oxide (C.I. Pigment Black 11); and aniline black (C.I. Pigment Black 1).
Specific examples of the color pigments preferably used in the present invention includes C.I. Pigment Yellow 1 (Fast Yellow G), 3, 12 (Disazo Yellow AAA), 13, 14, 17, 24, 34, 35, 37, 42 (yellow iron oxide), 53, 55, 81, 83 (Disazo Yellow HR), 95, 97, 98, 100, 101, 104, 108, 109, 110, 117, 120, 138, and 153; C.I. Pigment Orange 5, 13, 16, 17, 36, 43, and 51; C.I. Pigment Red 1, 2, 3, 5, 17, 22 (Brillant Fast Scarlet), 23, 31, 38, 48:2 (Permanent Red 2B (Ba)), 48:2 (Permanent Red 2B (Ca)), 48:3 (Permanent Red 2B (Sr)), 48:4 (Permanent Red 2B (Mn)), 49:1, 52:2, 53:1, 57:1 (Brilliant Carmine 6B), 60:1, 63:1, 63:2, 64:1, 81 (Rhodamine 6G Lake), 83, 88, 101 (iron oxide red), 104, 105, 106, 108 (Cadmium Red), 112, 114, 122 (Quinacridone Magenta), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 185, 190, 193, 209, and 219; C.I. Pigment Violet 1 (Rhodamine Lake), 3, 5:1, 16, 19, 23, and 38; C.I. Pigment Blue 1, 2, 15 (Phthalocyanine Blue R), 15:1, 15:2, 15:3 (Phthalocyanine Blue E) 16, 17:1, 56, 60, and 63; and C.I. Pigment Green 1, 4, 7, 8, 10, 17, 18, and 36.
Further, a pigment such as carbon black may be surface-treated with a resin to prepare a graft pigment which can be dispersed in water, and surface-treated with a functional group such as a sulfonate group or a carboxyl group so as to be dispersed in water.
Furthermore, the pigment may be included in microcapsule to be dispersed in water.
When the black pigment is added to the formulation for the ink composition, it is preferable that the black pigment be dispersed in an aqueous medium using a dispersant to prepare a black pigment dispersion. The black pigment dispersion thus prepared may be added to the formulation for the recording ink composition. Any dispersants for preparing conventional pigment dispersions can be used.
Examples of the dispersant include polyacrylic acid, polymethacrylic acid, acrylic acidxe2x80x94acrylonitrile copolymer, vinyl acetatexe2x80x94acrylic ester copolymer, acrylic acidxe2x80x94alkyl acrylate copolymer, styrenexe2x80x94acrylic acid copolymer, styrenexe2x80x94methacrylic acid copolymer, styrenexe2x80x94acrylic acidxe2x80x94alkyl acrylate terpolymer, styrenexe2x80x94methacrylic acidxe2x80x94alkyl acrylate terpolymer, styrenexe2x80x94xcex1-methyl styrenexe2x80x94acrylic acid terpolymer, styrenexe2x80x94xcex1-methyl styrenexe2x80x94acrylate terpolymer, styrenexe2x80x94maleic acid copolymer, vinyl naphthalenexe2x80x94maleic acid copolymer, vinyl acetatexe2x80x94ethylene copolymer, vinyl acetatexe2x80x94fatty acid vinyl ethylene copolymer, vinyl acetatexe2x80x94maleic acid ester copolymer, vinyl acetatexe2x80x94crotonic acid copolymer, and vinyl acetatexe2x80x94acrylic acid copolymer.
In the presence invention, those copolymers and terpolymers of dispersants have a weight average molecular weight of 5,000 to 100,000, preferably 6,000 to 50,000, more preferably 7,000 to 30,000, and further preferably 8,000 to 15,000. The dispersant may be appropriately added to the pigment in such an amount that can stably disperse the pigment, in view of the advantages of the present invention. Specifically, the ratio by weight of the pigment to the dispersant is preferably in a range of (1:0.06) to (1:3), and more preferably (1:0.125) to (1:3).
The ink composition of the present invention comprises water as a medium. To obtain desired ink properties, prevent the ink from drying, and improve the solution stability, a water-soluble organic solvent is used in combination with water.
Specific examples of the water-soluble organic solvent for use in the present invention include polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glygol, tetraethylene glycol, hexylene glycol, polypropylene glycol, 1,5-pentanediol, 1,6-hexanediol, glycerol, 1,2,6-hexanetriol, 1,2,4-butanetriol, 1,2,3-butanetriol, and 3-methyl-pentane-1,3,5-triol; alkyl ethers derived from polyhydric alcohols such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether; aryl ethers derived from polyhydric alcohols such as ethylene glycol monphenyl ether, and ethylene glycol monobenzyl ether; nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethylimidazolidinone, xcex5-caprolactam, and xcex3-butyrolactone; amides such as formamide, N-methylformamide, and N,N-dimethylformamide; amines such as monoethanol amine, diethanol amine, triethanol amine, monoethylamine, diethylamine, and triethylamine, sulfur-containing compounds such as dimethyl sulfoxide, sulfolane, and thiodiethanol; propylene carbonate; and ethylene carbonate. Those water soluble organic solvents may be used alone or in combination.
Of those water-soluble organic solvents, there are preferably employed diethylene glycol, thiodiethanol, polyethylene glycol (200 to 600), triethylene glycol, glycerol, 1,2,6-hexanetriol, 1,2,4-butanetriol, 3-methylpentane-1,3,5-triol, 1,5-pentanediol, 2-pyrrolidone, and N-methyl-2-pyrrolidone. Such organic solvents can effectively work not to lower the ink ejecting properties. Further, when the water-soluble organic solvent comprises at least one pyrrolidone derivative, in particular, 2-pyrrolidone, the quality of the obtained ink image can be improved.
As the wetting agent for use in the ink composition of the present invention, glycerin is preferably used. It is preferable that the ratio by weight of the wetting agent to the water-soluble organic solvent be in the range of (10:1) to (1:10) for imparting the well-balanced properties to the ink composition. In the case where glycerin is used as the wetting agent and diethylene glycol is used as the water-soluble organic solvent, the ratio by weight of the wetting agent to the water-soluble organic solvent is preferably within the range of (4:1) to (1:4). Other solvents than water, that is, a mixture of the water soluble organic solvent, wetting agent, and 2-ethyl-1,3-hexanediol is preferably contained in an amount of 1 to 30 wt. % of the total weight of the ink composition.
It is preferable that the ink composition of the present invention have a dynamic surface tension of 50 mJ/m2 or less, more preferably 40 mJ/m2 or less to obtain excellent drying characteristics of the ink image.
The surface tension of the recording ink composition can be used as an indication of the penetration properties of the ink composition into a recording paper. The surface tension means a dynamic surface tension measured within a short period of one second or less after the formation of the surface of a droplet on the recording paper.
The above-mentioned dynamic surface tension of the recording ink composition can be measured by any of the conventional methods, for example, by the method described in Japanese Laid-Open Patent Application No. 63-31237 herein incorporated by reference. In the present invention, the dynamic surface tension is determined by use of the Wilhelmy""s surface balance.
For the purpose of adjusting the surface tension of the recording ink composition of the present invention, the above-mentioned polyols and/or glycol ethers may be employed. Further, following can also be employed: alkyl and aryl ethers derived from polyhydric alcohols such as diethylene glycol monophenyl ether, ethylene glycol monophenyl ether, ethylene glycol monoallyl ether, diethylene glycol monobutyl ether, propylene glycol monobutyl ether, and tetraethylene glycol chlorophenyl ether; anionic surfactants; nonionic surfactants; fluorine-containing surfactants; and lower alcohols such as ethanol and 2-propanol. Especially preferred is diethylene glycol monobutyl ether.
The recording ink composition of the present invention may further comprises a resin emulsion. The resin emulsion for use in the present invention is an emulsion constituted by a continuous phase comprising water and a disperse phase comprising a resin. Examples of the resin for use in the resin emulsion are an acrylic resin, a vinyl acetate resin, a styrenexe2x80x94butadiene resin, a vinyl chloride resin, an acrylicxe2x80x94styrene resin, a butadiene resin, and a styrene resin.
It is preferable that the above-mentioned resin be a polymer having both a hydrophilic moiety and a hydrophobic moiety. The particle diameter of the resin for use in the resin emulsion is not particularly limited, but preferably about 150 nm or less, and more preferably about 5 to 100 nm.
The resin emulsion can be obtained by mixing the resin particles and water, with a surfactant being optionally added thereto. A self-dispersion type emulsion due to the presence of a hydrophilic group such as hydroxyl group can be prepared by using no surfactant. For example, an emulsion of an acrylic resin or a styrenexe2x80x94acrylic resin can be obtained by mixing (meth)acrylic ester or a mixture of styrene and (meth)acrylic ester, and water, with a surfactant being optionally added thereto. The ratio by weight of the resin to the surfactant is preferably in a range of about (10:1) to (5:1). Within the above-mentioned range, the resin is easily emulsified, and the water resistance and the penetrating properties of the obtained ink composition do not decrease.
For the preparation of the resin emulsion, it is proper that the amount of water be 60 to 400 parts by weight, preferably 100 to 200 parts by weight, with respect to 100 parts by weight of the resin.
There are various commercially available resin emulsions, for example, xe2x80x9cMicro Gel E-1002xe2x80x9d and xe2x80x9cMicro Gel E-5002xe2x80x9d (Trademark), which are styrenexe2x80x94acrylic resin emulsions manufactured by Niopon Paint Co., Ltd.; xe2x80x9cBoncoat 4001xe2x80x9d and xe2x80x9cBoncoat 5454xe2x80x9d (Trademark), which are respectively an acrylic resin emulsion and a styrenexe2x80x94acrylic resin emulsion, manufactured by Dainipoon Ink and Chemicals, Incorporated; xe2x80x9cSAE-1014xe2x80x9d (Trademark), which is a styrenexe2x80x94acrylic resin emulsion manufactured by Nippon Zeon Co., Ltd.; and xe2x80x9cSaibinol SK-200xe2x80x9d (Trademark), which is an acrylic resin emulsion manufactured by Saiden Chemical Industry Co., Ltd.
It is preferable that the resin emulsion comprise their resin component in an amount of 0.1 to 40 wt. %, more preferably 1 to 25 wt. % of the total weight of the ink composition.
The resin emulsion tends to thicken, thereby inhibiting the colorant from spreading and promoting the fixing properties of ink images to the recording material. When the ink composition is deposited on a recording material to form an ink image thereon, the resin emulsion for use in the ink composition can form a film on the recording material according to the kind of resin emulsion. In this case, the abrasion resistance of the obtained printed matter can be improved.
The recording ink may further comprise a sugar. Examples of the sugar are monosaccharide, disaccharide, oligosaccharide (including trisaccharide and quadrisaccharide), and polysaccharide. Preferable examples of the sugar for use in the present invention include glucose, mannose, fructose, ribose, xylose, arabinose, galactose, maltose, cellobiose, lactose, sucrose, trehalose, and maltotriose. The polysaccharides herein use include the substances occurring in nature such as xcex1-cyclodextrin and cellulose.
Derivatives of those sugars can also be used for the ink composition. There are, for example, reducing sugars such as sugar alcohol represented by general formula of HOCH2(CHOH)nCH2OH, wherein n is an integer of 2 to 5, oxidized sugars such as aldonic acid and uronic acid, amino acids, and thioacids. In particular, the sugar alcohols, i.e., maltol and sorbitol are preferred. It is proper that the sugar be contained in an amount of 0.1 to 40 wt. %, preferably 0.5 to 30 wt. % of the total weight of the recording ink composition:
The recording ink composition of the present invention may further comprise any conventional additives such as a preservative, pH controlling agent, chelating agent, and rust inhibitor.
Examples of the preservatives include sodium dehydroacetate, sodium sorbate, sodium 2-pyridine thiol-1-oxide, sodium benzoate, and pentachloro sodium phenolate.
As the pH controlling agent, any materials can be used as long as the ink composition can be adjusted to pH 7 or more without being adversely affected. Examples of the pH controlling agent for use in the present invention include amines such as diethanolamine and triethanolamine; hydroxides of alkali metal such as lithium hydroxide, sodium hydroxide, and potassium hydroxide, and other hydroxides such as ammonium hydroxide, quaternary ammonium hydroxide, and quaternary phosphonium hydroxide; and alkali metal carbonates such as lithium carbonate, sodium carbonate, and potassium carbonate.
Examples of the chelating agent for use in the ink composition include sodium ethylenediamine tetraacetate, sodium nitrilotriacetate, sodium hydroxethyl ethylenediamine triacetate, sodium diethylenetriamine pentaacetate, and sodium lauryl diacetate.
Examples of the rust inhibitor include acid sulfite, sodium thiosulfate, antimony thiodiglycolate, diisopropyl ammonium nitrite, pentaerythritol tetranitrate, dicylochexyl ammonium nitrite.
In addition, a water-soluble ultraviolet absorber, a water-soluble infrared absorber, and a surfactant other than the aforementioned surfactants (I) to (V) may be added to the recording ink composition, as required.
Other features of this invention will become apparent in the course of the following description of exemplary embodiments, which are given for illustration of the invention and are not intended to be limiting thereof.